// для опроса

function addField(btn) {
        tr = btn;
        while (tr.tagName != 'TR') tr = tr.parentNode;
        var newTr = tr.parentNode.insertBefore(tr.cloneNode(true),tr.nextSibling);
        checkFieldForLast();
}

function checkFieldForLast() {
        btns = document.getElementsByName('drop_answer');
        for (i = 0; i < btns.length; i++){
            btns[i].disabled = false;
        }
        if (btns.length<=2) {
            btns[0].disabled = true;
            btns[1].disabled = true;
        }
}

function dropField(btn) {
        tr = btn;
        while (tr.tagName != 'TR') tr = tr.parentNode;
        tr.parentNode.removeChild(tr);
        checkFieldForLast();
}